An investigation of the kinetics of reduction of dense synthetic nickel oxide has been carried out in H2-N2 and H2-H2O mixtures between 500 °C and 1000 °C. The progress of the reduction was followed metallographically by the measurement of the advance of the nickel product layer. The influences of hydrogen partial pressure, hydrogen-steam ratio, and temperature were systematically investigated in both sets of the mixtures. Increasing hydrogen partial pressure under all conditions investigated results in an increase in the reduction rate. In H2-N2 mixtures and H2-H2O mixtures with low steam content, the initial reduction rate was found to be first order with respect to hydrogen partial pressure. In both sets of mixtures, it was found that the progress of Ni thickness was not a monotonic function of temperature. A minimum rate of advancement of Ni product was observed between 600 °C and 800 °C, depending on the hydrogen partial pressures and reduction time. The change in reduction behavior is shown to be directly linked to changes in Ni product microstructure.